1. Field of the Invention
The present invention relates to an oil pressure generator and a power output apparatus. More specifically the present invention pertains to an oil pressure generator for producing an oil pressure by means of rotational power given to an input shaft and a power output apparatus with such an oil pressure generator for outputting power to a drive shaft.
2. Description of the Related Art
Known oil pressure generators mounted on a vehicle are attached either directly or indirectly to a crankshaft of an engine (for example, an internal combustion engine like a gasoline engine or a diesel engine), which is one constituent of a transmission mechanism, for the purpose of feeding a supply of oil to a torque converter, lubricating a planetary gear unit included in the transmission, and supplying a working oil pressure to regulate the oil pressure in the transmission. The known oil pressure generators are driven by part of rotational power output from the engine to the crankshaft. The proposed oil pressure generator is, for example, constructed as a gear pump unit 200 illustrated in FIG. 11, which includes a casing 220, a drive gear 230 connected with the crankshaft, a driven gear 232 engaging with the drive gear 230 for rotation, and a crescent 234 interposed between the drive gear 230 and the driven gear 232. In this known structure, an oil pressure is produced through rotations of the drive gear 230 and the driven gear 232 that are accompanied by rotation of a drive shaft. An oil inflow conduit 224 and an oil outflow conduit 226 are formed in the casing 220.
Hybrid electric vehicles with an engine, a generator, a motor, and a battery mounted thereon have been proposed recently to preserve the environment and efficiently utilize the valuable energy resources. The hybrid electric vehicle can be driven only by the power output from the engine, only by the power output from the motor, or by the powers output from both the engine and the motor. An oil pressure generator is also required for the hybrid electric vehicles, in order to lubricate a gear unit in case that the crankshaft of the engine is linked with a drive shaft connecting with driving wheels via the gear unit, in order to actuate a clutch in case that the crankshaft of the engine is linked with the drive shaft via the clutch, and in order to lubricate a gear unit, such as a speed change gear.
One possible technique attaches the gear pump unit 200 functioning as an oil pressure generator to the crankshaft of the engine on the hybrid electric vehicle. While the engine is in operation, the oil pressure generator produces an oil pressure. When the vehicle is driven only by the power output from the motor and the engine is at a stop, however, the oil pressure generator does not produce an oil pressure to actuate the clutch or lubricate the gear unit. Another possible technique attaches the gear pump unit 200 to the drive shaft and enables an oil pressure to be produced by rotational power of the drive shaft. In this case, however, the oil pressure generator does not produce an oil pressure while the vehicle is at a stop.
These problems arise not only on the vehicle with the engine and the motor mounted thereon but on any driving systems driven by powers output from two or more power sources.
The applicant of the present invention has proposed the structure of attaching an oil hydraulic pump to the crankshaft of the engine on a hybrid electric vehicle with a gear unit (JAPANESE PATENT LAYING-OPEN GAZETTE No. 50-30223) as well as the structure of attaching oil hydraulic pumps respectively to the crankshaft of the engine and the drive shaft (JAPANESE PATENT LAYING-OPEN GAZETTE No. 48-49115).